The present invention relates to a technology for manufacturing a resin molded or encapsulation type semiconductor device using a lead frame, and particularly to a technology effective for application to the manufacture of a semiconductor device wherein external electrode terminals (leads) are exposed to the mounting surface side as in an SON (Small Outline Non-Leaded Package) and a QFN (Quad Flat Non-Leaded Package).
A resin encapsulation type semiconductor device makes use of a lead frame upon its manufacture. The lead frame is fabricated by forming a metal plate as a desired pattern by punching using a precision press or etching. The lead frame has a support portion called a xe2x80x9ctub or the likexe2x80x9d for fixing a semiconductor chip, and a plurality of leads whose leading ends (internal ends) face the periphery of the support portion. The tub is supported by tub-suspension leads which extend from a frame portion of the lead frame.
When the resin encapsulation type semiconductor device is fabricated through the use of such a lead frame, the semiconductor chip is fixed to the tub of the lead frame, and electrodes of the semiconductor chip and leading ends of the leads are connected to one another by conductive wires. Afterwards, the lead internal-end side including the wires and the semiconductor chip is sealed with an insulating resin to thereby form an encapsulater (package). Further, an unnecessary lead frame portion is removed by cutting, and the leads and tub-suspension leads protruding from the package are cut. Each of the leads is brought to a flat state or processed into a predetermined shape.
As technologies for solving a problem as to a transfer mold for forming a resin encapsulation package, there are known technologies described in Unexamined Patent Publication Nos. Hei 5(1993)-326799, 2000-61989 and Hei 5(1993)-299455, for example.
Although a resin injection hole (gate) is not illustrated in the drawing in the above technologies, the prior art set forth as a premise has described that the resin injection hole is provided in a lower mold. Accordingly, a resin (called xe2x80x9cgate cured resinxe2x80x9d) cured at a gate portion extends on one surface side of a lead frame so as to have a predetermined height.
Unexamined Patent Publication No. 2000-61989 has disclosed the technology of separating a runner from a molded plastic package with being flush with the package upon a transfer mold process. Namely, a transfer mold die has a movable gate lowered so as to make contact with the plastic package formed at a resin inlet for the cavity on the same plane as the plastic package before the resin is cured after having been injected in the cavity. Accordingly, the runner can be cut on a flush basis with the plastic package.
The same reference has described that when the resin cured within the runner is removed, the resin cured at the runner portion remains at each edge of the plastic package, and a bottleneck is produced in the subsequent lead formation and trimming process due to such a remainder. Problems will be quoted from the same reference and described below.
(1) Damage is put on the trimming of each lead and the formation of a die, and manufacturing yields and a production throughput are reduced. It is necessary to repair or fix up an expensive die.
(2) There is a possibility that upon lead trimming and forming processes, the plastic package will be peeled off from the lead frame, thereby causing a problem about the reliability of a completed product.
(3) The adhesion of the remainder or remaining materials to the plastic package as it is will lead to a serious result. Described typically, a check is made to respective packages and all the remaining materials are manually removed. Therefore, personnel costs increase and a manufacturing throughput is reduced.
According to the present technology, runner""s fragments are not left behind with being attached to the plastic package even after the transfer mold. Further, the runner can be detached from the molded lead frame. Thus the work of manually removing the remainder becomes unnecessary. It is also possible to avoid damage to the trimming of each lead and a lead forming instrument due to the remainder as well as to avoid damage to a packaged semiconductor device.
The present technology shows the technical idea that since the remainder of the resin produces a bottleneck in the trimming process such as the bending of each lead, the occurrence of the remainder in the lead frame is avoided even after the removal of the runner. The present technology has no description about the cutting of leads at a gate portion, i.e., a basal portion of the package and makes little mention of such a problem.
Unexamined Patent Publication No. Hei 5(1993)-299455 describes the technology of thinning a gate in stepped form in advance at a base of a resin encapsulated portion so that when a resin portion cured at a gate portion for forming the resin molded portion is separated from a package, a gate residual is not much left on a placed piece or fragment, and causing a gate cured resin to remain on the placed piece thinner or shorter upon removal of the gate cured resin.
The present technology does not show the idea of cutting a placed-fragment portion causing the remainder of the gate.
On the other hand, as one resin encapsulation type semiconductor device fabricated using a lead frame, there is known a non-leaded type semiconductor device such as an SON, a QFN or the like adopted or taken as a semiconductor device structure wherein one surface of the lead frame is single-sided molded to thereby form a package, and leads corresponding to external electrode terminals are exposed to the mounting surface side of the package, thereby avoiding the intentional protrusion of the leads from the peripheral surface of the package.
In terms of a size reduction in semiconductor device, the prevention of bending of leads corresponding to external electrode terminals, etc., a non-leaded type semiconductor device such as a single-sided molded SON or QFN has been used.
Since the outer shape of the non-leaded type semiconductor device is principally determined depending on a resin encapsulater (package) and a lead cutting castle or castled extension formed on its periphery, the semiconductor device can be reduced in size as compared with a semiconductor device of such a type that leads are placed on the periphery of a package, generally called a xe2x80x9cQFP (Quad Flat Package)xe2x80x9d or an SOP (Small Outline Package)xe2x80x9d. The lead cutting castle or castle extension is produced by ensuring an area for applying a die between a cutting-plane line and a package when the leads are cut by punches, and is formed with a width of about 0.1 mm in the embodiment of the present specification, for example.
Problems about the manufacture of the conventional single-sided molded non-leaded type semiconductor device will now be explained.
A description will first be made of one in which a resin encapsulater (package) is formed on one surface side of a lead frame by a transfer mold with the manufacture of QFN as an example.
FIG. 31 is a plan view showing a resin encapsulater formed by a transfer mold and a unit lead frame pattern. As shown in the same drawing, a lead frame 1 has a structure having a frame portion 2 shaped in the form of a rectangular frame, a plurality of leads 3 extending inwardly from inside the respective sides of the frame portion 2, and tub-suspension leads 4 (only one tub-suspension lead is shown in the drawing) which respectively extend inwardly of the frame portion from the four corners of the frame portion 2 and support a central tub (not shown). A resin encapsulater (package) 5 is formed in a central portion of a unit lead frame pattern 6, and leading end portions (internal end portions) of the respective leads 3 extend within the package 5. Lower surfaces of the leads 3 are exposed from the package 5. The exposed lead portions serve as external electrode terminals for surface mounting when a semiconductor device is brought about.
Although not illustrated in the drawing, a semiconductor chip fixed onto the tub is placed within the package 5. Further, electrodes of the semiconductor chip and inner ends of the leads 3 are electrically connected to one another by conductive wires.
Upon a transfer mold, a gate (G) is located in one corner (corresponding to the upper right corner in FIG. 31) of the lead frame 1. A resin is injected into a cavity of a mold die through the gate to thereby form the corresponding package 5. At this time, air lying within the cavity escapes from air vents (E) located in the remaining three corners of the lead frame 1 to the outside of the mold die. Thus, the resin enters even the gate and the air vents and hence the resin at these portions is also cured by resin""s curing. The resin cured at the gate portion will be referred to as a xe2x80x9cgate cured resin 7xe2x80x9d below. The resins cured at the air vent portions will be called xe2x80x9cair vent cured resins 9xe2x80x9d.
The package 5 shaped in rectangular form is generally chamfered as shown in FIG. 31 to have slopes 8 in such a way as to avoid the presence of cornered portions (corners). The slopes 8 are large in gate portion and small in air vent portions.
After the transfer mold, the resin cursed inside each runner for guiding the resin is removed when the curing of the resin is finished. FIG. 31 shows a state in which a runner cured resin or the like is removed and is a diagram showing that the gate cured resin 7 and the air vent cured resins 9 remain.
FIG. 32 is a side view typically showing the lead frame 1, package 5, air vent cured resins 9, runner cured resin 10 and gate cured resin 7. FIG. 33 is a typical cross-sectional view showing the lead frame 1, tub-suspension leads 4, package 5 and gate cured resin 7 or the like. As shown in FIG. 32, the resin cured at the gate portion upon removal of the runner cured resin 10 is formed integrally with the package 5. Therefore, the resin will break in the course thereof and a gate cured resin 7 of a chevron or mounting type as viewed from the side remains. Namely, as the gate cured resin 7 is kept away from the package 5, the thickness thereof becomes thick and its leading end is brought to a broken state.
Thus, even when the gate cured resin 7 is set to such a shape that its thickness becomes thick as it is distant from the package, and is designed in such a manner that the gate cure resin is preferably broken in the vicinity of the package upon breakage and removal of the gate cured resin, the gate cured resin cannot be prevented perfectly from remaining, and the size and shape of the produced remaining cured resin are made in various ways.
As shown in FIG. 33, the cured resins remain on both sides of the tub-suspension lead 4 as indicated by dots. Namely, upon the transfer mold, spaces defined by parting surfaces of upper and lower molds of a mold die and the tub-suspension lead 4 and leads 3 adjacent thereto both located at the gate portion are formed as spaces which communicate with the gate. The cured resins having entered the spaces correspond to the cured resin portions indicted by the dots. These cured resin portions are generally called resin burrs 11. The thickness of each resin burr 11 is identical to that of each lead 3 in a state in which the parting surfaces of the upper and lower molds of the mold die are closely bonded to the obverse and reverse sides of the lead frame.
However, when a gap is defined between each of the parting surfaces and the lead frame where the above package is clamped between the parting surfaces of the upper and lower molds of the mold die and the lead frame, the resin enters into the gap and so-called resin flashes occur in each lead surface or the like. In the resin-flash generated state, the thickness of each resin burr 11 becomes thicker than that of each lead.
After the transfer mold, the leads 3 and tub-suspension leads 4 both protruding from the periphery of the package are cut at the peripheral edge of the package 5, whereby the corresponding non-leaded type semiconductor device (QFN) is manufactured. When, at this time, the sizes of the gate cured resin 7 and each air vent cured resin 9 are too large to accommodate or hold them in the lead cutting castle, the gate cured resin 7 and the air vent cured resins 9 are also cut upon lead cutting.
FIG. 34 is a typical view showing the situation in which a gate cured resin 7 and air vent cured resins 9 are cut by a die 15 and punches 16 together with each tub-suspension lead 4. The cutting of leads 3 is also carried out by a die and punches each having a similar structure.
However, when the gate cured resin 7 remains at one side of a package as shown in FIG. 34, it is essential that the gate cured resin 7 is cut while the die 15 is being applied to the mounting surface side contrary to the normal lead cutting. This is because since the flatness of each lead surface on the package side is lost due to the presence of the gate cured resins 7, and the remaining amounts thereof are all different, the die 15 cannot be stably applied to each lead.
It turned out that since the gate cured resin 7 takes such a shape as to protrude toward its corresponding punch 16 as described above, the gate cured resin 7 firstly contacts the punch 16 and thereby stress is applied to the punch 16 upon cutting as shown in FIG. 35, whereby breakage, cracks and chipping are developed therein by stress concentration and resin waste is frequently produced.
It has been found that the resin waste 17 is spattered over the periphery and is thereby attached not only to other lead frame portions but also to surfaces related to the cutting of the die 15 and punches 16 and cut surfaces of the gate cured resin 7 and tub-suspension lead 4 as shown in FIG. 34. Namely, the resin waste is produced by (1) cutting away the resin in fine form when the punches are applied to the gate cured resins as described above and (2) rubbing the punches and their cut surfaces against each other when the punches are returned to their predetermined positions after their cutting. Further, the resin waste drops out even by vibrations at the carrying of a product, contaminates a cutting die and is re-attached to other product portions.
In the non-leaded type semiconductor device, there is a fear that since each lead surface exposed to the back of the package is brought to the external electrode terminal surface so as to serve as a mounting surface, an electrically-isolated state occurs in a mounted state when the insulative resin waste is attached or crimped to the surface, thereby interfering with a stable operation of the semiconductor device.
When the gate cured resin is much cracked upon its cutting, a crack enters even into the package, thereby causing a reduction in moisture resistance and degradation of reliability.
If a method of applying the die 15 to the mounting surface side of each lead with a cutting-plane line interposed therebetween and cutting the leads by the punches 16 from the side opposite to the mounting surface is adopted as shown in FIG. 34, then cut burrs occur in the mounting surface of each lead, thereby losing the flatness of the mounting surface and degrading reliability.
A non-leaded type semiconductor device has heretofore been fabricated according to a method shown by such a flowchart as shown in FIG. 36. The non-leaded type semiconductor device is manufactured via respective process steps of Steps 201 through 207. Namely, after the commencement of work, the semiconductor device is fabricated via the respective process steps of chip bonding (S201), wire bonding (S202), molding (S203), gate pre-cutting (S204), plating (S205), pinch-cut by composite cut molding (S206), and lead tip cutting (S207), and thereafter the work is finished.
In the present manufacturing method, the gate pre-cutting (S204) is carried out before the plating step, and each gate-portion tub-suspension lead is punched out to a predetermined length. Therefore, even if resin waste occurs, the resin waste is removed by cleaning corresponding to processing subsequent to the plating. Thus, a problem about the above-described resin waste little arises.
However, the present manufacturing method is accompanied by a drawback that as a cutting process executed by a press machine, the gate pre-cutting (S204), the pinch-cut (S206) by composite cut molding, and the lead tip cutting (S207) are carried out twice, thereby increasing the manufacturing cost of a semiconductor device.
Thus the present applicant adopts a manufacturing method of achieving a reduction in manufacturing cost with the press machine-based cutting process as one. FIG. 37 is a flowchart using the present manufacturing method.
A non-leaded type semiconductor device is manufactured via respective process steps of Steps 301 through 307. Namely, after the commencement of work, the semiconductor device is fabricated via the respective process steps of chip bonding (S301), wire bonding (S302), molding (S303), plating (S304), gate crush by composite cut molding (S305), pinch-cut (S306) and lead tip cutting (S307), and thereafter the work is completed.
A composite cut mold is attached to one press machine. Under intermittent motion of a lead frame and a cutting operation based on composite cut molding, the cutting (corresponding to the gate crush for cutting one point in linear form) of a gate portion and tub-suspension leads thereof, pinch-cutting for cutting remaining tub-suspension leads used to support a package, and lead tip cutting for cutting all the leads at the basal portion of the package are executed to complete a semiconductor device, and thereafter the work is finished.
FIGS. 38(a) and 38(b) are respectively typical views showing a gate crush operation. In a manufacturing method using gate crush, processing is done in a state in which a package 5 is placed on a lower surface of a lead frame 1.
Namely, a die 15 is placed on the upper side of the lead frame 1. A punch 16 goes up from its lower side to cut a gate cured resin 7 and each tub-suspension lead 4 extending together with the gate cured resin 7. The punch 16 serves like a knife edge without having a structure for cutting them to a predetermined length and simply cuts the gate cured resin 7 and each tub-suspension lead 4. The tub-suspension lead 4 is bent as shown in FIG. 38(a) under the post-cut moving operation of the punch 16. Resin waste 17 is produced even upon the cutting of the gate cured resin 7 and the tub-suspension lead 4.
Owing to the execution of such gate crush processing, the cutting of the gate cured resin and each tub-suspension lead thereat at pinch-cutting (S306) become unnecessary, and the produced amount of resin waste can be reduced. An advantage is brought about in that it is possible to reduce a resin crack produced in the gate portion and a cut failure in tub-suspension lead.
However, it has been found that in the case of the present gate crush, the cut resin surface and the die are rubbed against each other when the cut type (die) is opened as shown in FIG. 38(b), so that resin waste is spattered, thereby causing adhesion to each lead surface. An arrow in FIG. 38(b) is used to indicate the situation in which the resin waste 17 is spattered upon die opening to thereby adhere onto each lead (while the lead corresponds to the tub-suspension lead in the drawing, unillustrated leads are also arranged on this surface of the package 5).
An object of the present invention is to provide a technology wherein when a gate cured resin and air vent cured resins are cut upon the manufacture of a non-leaded type semiconductor device fabricated by a single-sided mold, resin waste is restrained from occurring to thereby prevent the attachment of the resin waste to external electrode terminals.
Another object of the present invention is to provide a technology wherein when a gate cured resin and air vent cured resins are cut upon the manufacture of a non-leaded type semiconductor device fabricated by a single-sided mold, a resin crack is retrained from occurring to thereby prevent a reduction in moisture resistance of the semiconductor device and the occurrence of a failure in outward appearance thereof.
The above, other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.
Summaries of typical ones of the inventions disclosed in the present application will be described in brief as follows:
(1) There is provided a semiconductor device which has an encapsulater comprising an insulating resin, leads and tub-suspension leads exposed to a mounting surface of said encapsulater and a gate cured resin and air vent cured resins which remain as a result to form said encapsulater, and wherein each of the gate cured resin and the air vent cured resins exists in a portion between each tub-suspension lead and each lead with a thickness identical to or smaller than the thickness of each of resin burrs.
Such a semiconductor device is manufactured by the following manufacturing method.
There is provided a method of manufacturing a semiconductor device, comprising a step for preparing a lead frame having a frame portion, a plurality of leads which protrude inwardly of the frame portion from the frame portion, and a plurality of tub-suspension leads which protrude inwardly of the frame portion from the frame portion and support a tub at leading end portions thereof; a step for fixing a semiconductor chip to one surface of the tub; a step for electrically connecting electrodes of the semiconductor chip and the leads; a step for covering the semiconductor chip and the leads with an encapsulater comprising an insulating resin and exposing the leads and the tub-suspension leads to a mounting surface of the encapsulater; and a step for cutting the leads and the tub-suspension leads; and wherein a vertical space defined by only the sides of the leads and the tub-suspension leads is used as a resin flow path to form the encapsulater, and the leads and the tub-suspension leads are cut at a resin portion cured in the vertical space defined by only the sides of the leads and the tub-suspension leads.
Further, a gate provided in a mold die is provided outside the vertical space defined by only the sides of the leads and the tub-suspension leads, and a resin passes through the gate and flows through the vertical space to thereby form the encapsulater. In addition, air vents defined in the mold die are provided outside the vertical space defined by only the sides of the leads and the tub-suspension leads, and the resin passes through the vertical space and goes through the air vents.
According to the means of (1) referred to above, (a) The cutting of leads and tub-suspension leads that protrude from the periphery of an encapsulater (package), and the cutting of gate cured resins and air vent cured resins produced upon the formation of the package are performed at portions respectively identical in thickness and whose front and back are flat. Thus, they can be cut by punches and a die without partly applying an on-cutting stress on the gate cured resins and air vent cured resins in a large way. It is therefore possible to reduce the occurrence of resin waste to a large extent as compared with the conventional cutting method and restrain the occurrence of a resin crack.
(b) Since the resin waste can be restrained from occurring, the attachment and crimping of the resin waste to lead surfaces serving as external electrode terminals due to the spattering of the resin waste, and the occurrence of flaws caused by the crimping can be restrained. It is also possible to ensure solderability at mounting and enhance mounting yields. Furthermore, the reliability of the mounting or implementation of a non-leaded type semiconductor device can be improved.
(c) Since a matrix type lead frame takes a structure wherein unit lead frame patterns are vertically and horizontally arranged in line, the prevention of the spattering of the resin waste results in the prevention of contamination of the resin waste on each unit lead frame pattern around a predetermined unit lead frame pattern, whereby production yields can be improved to a great extent.
(d) Since the occurrence of the resin waste can be restrained, the contamination caused by the cut-die""s resin waste can be prevented from occurring, and the availability factor of a press machine for mounting a cut die can be improved.
(e) Since the gate cured resins and air vent cured resins around the package are rendered integral with resin burrs between adjacent leads or those between tub-suspension leads and leads and are identical to the resin burrs in obverse and reverse sides, it is difficult to visually confirm the gate cured resins and air vent cured resins on the periphery of the package of the non-leaded type semiconductor device. Thus, the semiconductor device is look good and preferable even in outer appearance, and increases in commodity property.
(f) The manufacturing cost of a semiconductor device can be reduced in terms of productivity and an improvement in yield.